This invention relates to an apparatus and method to monitor flow passing through orifices or nozzle, and, more specifically, to an apparatus and method intended for use with a rewet shower or a steam-box for the paper making industry.
A modern paper machine turns pulp which is a mixture of water and fiber into paper through consecutive processes. Three sections of the machine which are named forming, pressing and drying play the most important roles in paper making. Normal pulp at the headbox contains about 1% fiber and 99% water.
The former section of the paper machine takes advantage of gravity and vacuum suction to remove water from the pulp and form a sheet thereafter. In the press section, the sheet is conveyed through a series of presses where additional water is removed and the fiber web is consolidated. The water concentration is reduced to about 40% after pressing. The remaining water is further evaporated and fiber bonding develops as the paper contacts a series of steam-heated cylinders in the drying section. The moisture level drops down to about 5% to 10% after the drying section.
One of the important properties of a paper product is the moisture level. Even more important than the absolute moisture level is the uniformity of moisture in the paper product in both the machine direction and the cross machine direction. A variation in moisture content of the sheet will often affect paper quality as much or more than the absolute moisture level. There are numerous influences on the paper machine that can cause variation of the moisture content, particularly in the cross machine direction. Wet edges and characteristic moisture profiles are common occurrences on paper sheets produced by a paper machine. Thus a number of commercially available actuator systems have been developed to offer control of the moisture profile during paper production.
One such actuator system is a water rewet shower that selectively adds water droplets onto the paper surface. The rewet showers employ actuator nozzle units that are mounted in sequential segments (or zones) across the paper machine direction. Water flow rate is controlled independently through each actuator nozzle unit. Hence the moisture profile on the paper sheet can be adjusted by the rewet system. Air-atomizing nozzles are normally used in those rewet showers to generate droplets small enough to produce rewet effectively.
The nozzles of the water rewet showers are normally positioned a few inches away from the paper sheet. There is a possibility that a nozzle orifice could be partially or fully blocked by fibers around the paper machine. Another potential problem is the wearing out of the nozzle orifice over time because the paper machine, and thus the spraying system, is operating around the clock. Variation of the nozzle orifice affects the flow characteristics of the nozzle, and consequently the performance of the spraying system.
Another such actuator system to control the moisture profile is a steam-box that is used on a paper machine to control paper moisture and to dewater. The steam box adds both moisture and heat to the paper surface. Adding water to the paper appears to be counterproductive, as the final purpose of the paper machine is to control the moisture to a relatively low level typically 5% to 10%. It is the heat that is added by the steam-box that accomplishes that result. Experiments show that heating the paper with steam allows the pressing process to remove much more water than that added by condensation of the steam.
Due to the ready availability and affordability of steam in most plants, devices using steam surpass those using other heat sources. Steam-boxes experience the same problem as a water spraying system. Fibers from outside of a steam-box can block the steam flow orifices and degrade the performance of the steam-box. There are many steam-box manufacturers around the world, but none has a device or methodology that can monitor the orifice status in the steam boxes.
The amount of flow passing through each segment (or zone) of a rewet shower or a steam-box is adjusted through an actuator located in that segment. An actuator is a device that converts an input signal into an output movement. The output movement then can be employed in a control mechanism. In the rewet shower and the steambox, water or steam is the medium to be controlled.
There are two types of actuators that can be used in a water rewet shower or a steam-box. One type converts a control signal to a linear movement. The linear movement is then employed to adjust proportionally an opening area in a valve mechanism. The flow amount passing through this valve is therefore controllable in a linear fashion by keeping the upstream flow pressure constant, and the varying opening area at the valve determines the flow rate.
The other actuator type is referred to as the regulator type. The regulator-type actuator regulates flow pressure feeding a constant opening based on a controlling reference pneumatic pressure. The varying pressure feeding the constant orifice determines the flow rate.
The regulator-type actuator is especially effective for applications requiring small flow control. It can be appreciated that precisely adjusting the opening of the small orifice is very difficult. Thus it is much easier to keep the small orifice untouched while regulating the flow pressure feeding that orifice.
Another important component in a rewet shower is the nozzle. Two kinds of nozzles, hydraulic and air atomizing, are widely used for water sprays. A hydraulic nozzle uses energy from a highly pressurized source to break water into droplets at the nozzle. The flow rate passing through a hydraulic nozzle is a function of the source pressure. The spraying pattern, such as spraying angle and velocity profile, is affected by the pressure as well. The fact that the droplet size is related to the flow rate makes the hydraulic nozzle ideal for operation at a fixed design point.
An air-atomizing nozzle uses energy from pressurized air to break water into small droplets. The spraying pattern is affected by air pressure only, and is independent of the water flow rate passing through the nozzle up to a certain point. The droplet size from an air-atomizing nozzle depends more on the air pressure than the water flow rate. Separating droplet size control from water flow control substantially simplifies the controlling strategy of a spraying system.
Water spraying rewet showers and steam-boxes both work under a dusty environment around paper machines. As was described above, the flow orifices in both systems are subject to fibers that could partially or completely block the flow passages. In addition the flow orifices will wear because the systems are normally operating around the clock for a long period of time. All of the existing rewet showers or steam-boxes do not Shave feedback mechanisms that can effectively monitor the status of the flow orifices.
Traditionally, pressure drop through a single orifice opening is measured for the calculation of the flow rate. This technique fails to work when the orifice opening area changes due to blockage or wear. Therefore a new technique had to be developed.
An actuator unit for controlling the flow of fluid from a source. The actuator unit has an atomizing nozzle and an actuator having a port for connection to a source of pneumatic control pressure. The atomizing nozzle has:
(i) a port for connection to a source of water, the actuator using the pneumatic control pressure to provide from the water source regulated water pressure to the atomizing nozzle;
(ii) a first orifice connected to the water port;
(iii) a second orifice downstream of the first orifice;
(iv) a first pressure port upstream of the first orifice for monitoring the regulated water pressure from the actuator; and
(v) a second pressure port located between the first orifice and the second orifice for monitoring the pressure between the first and the second orifices.
An atomizing nozzle having:
(a) a water inlet for providing regulated water pressure from a source of water to the atomizing nozzle;
(b) a first orifice connected to the water inlet;
(c) a second orifice downstream of the first orifice;
(d) a first pressure port upstream of the first orifice for monitoring the regulated water pressure from the actuator; and
(e) a second pressure port located between the first orifice and the second orifice for monitoring the pressure between the first and the second orifices.
An atomizing nozzle having:
(a) a nozzle body having a water inlet for providing regulated water pressure from a source of water to the atomizing nozzle;
(b) a first orifice connected to the water inlet;
(c) a second orifice downstream of the first orifice;
(d) a water nozzle tube in the nozzle body;
(e) a first chamber formed by the nozzle body and the first orifice and the second orifice for receiving the regulated water pressure from the water source;
(f) a second chamber downstream of the first chamber, the second chamber formed between the first orifice and the second orifice;
(g) a first pressure port connected to the first chamber for monitoring the regulated water pressure from the water source; and
(h) a second pressure port connected to the second chamber for monitoring the pressure between the first and the second orifices.
In an atomizing nozzle having:
(a) a nozzle body having a water inlet for providing regulated water pressure from a source of water to the atomizing nozzle;
(b) a first orifice connected to the water inlet;
(c) a second orifice downstream of the first orifice;
(d) a first pressure port located upstream of the first orifice; and
(e) a second pressure port located between the first orifice and the second orifice;
a method for determining the status of the first and the second orifices. The method has the steps of:
(i) measuring at the first pressure port the pressure upstream of the first and second orifices, the measured upstream pressure predetermining the pressure between the first orifice and the second orifice.
(ii) measuring at the second pressure port the pressure between the first and second orifices; and
(iii) determining a partial or whole blockage of the first orifice or the second orifice from the pressure measured at the first pressure port and the pressure measured at the second pressure port.